Understanding the linear and nonlinear optical responses of few-layer exfoliated MoS2and WS2nanoflakes: experimental and simulation studies.

Understanding the linear and nonlinear optical (NLO) responses of two-dimensional nanomaterials is essential to effectively utilize them in various optoelectronic applications. Here, few-layer MoS2and WS2nanoflakes with lateral size less than 200 nm were prepared by liquid-phase exfoliation, and their linear and NLO responses were studied simultaneously using experimental measurements and theoretical simulations. Finite-difference time-domain (FDTD) simulations confirmed the redshift in the excitonic transitions when the thickness was increased above 10 nm indicating the layer-number dependent bandgap of nanoflakes. WS2nanoflakes exhibited around 5 times higher absorption to scattering cross-section ratio than MoS2nanoflakes at various wavelengths. Open aperture Z scan analysis of both the MoS2and WS2nanoflakes using 532 nm nanosecond laser pulses reveals strong nonlinear absorption activity with effective nonlinear absorption coefficient (ßeff) of 120 cm GW-1and 180 cm GW-1, respectively, which was attributed to the combined contributions of ground, singlet excited and triplet excited state absorption. FDTD simulation results also showed the signature of strong absorption density of few layer nanoflakes which may be account for their excellent NLO characteristics. Optical limiting threshold values of MoS2and WS2nanoflakes were obtained as ∼1.96 J cm-2and 0.88 J cm-2, respectively, which are better than many of the reported values. Intensity dependent switching from saturable absorption (SA) to reverse SA was also observed for MoS2nanoflakes when the laser intensity increased from 0.14 to 0.27 GW cm-2. The present study provides valuable information to improve the selection of two-dimensional nanomaterials for the design of highly efficient linear and nonlinear optoelectronic devices.

Influence of Ag Nanostructure Location on the Absorption Enhancement in Polymer Solar Cells.

The optical absorption enhancement in Ag nanocube (NC)- and nanosphere (NS)-embedded poly[ N-9'-heptadecanyl-2,7-carbazole- alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]:[6,6]-phenyl C71-butyric acid methyl ester active layer was calculated using three-dimensional finite-difference time domain simulations. The simulations were carried out by incorporating Ag nanostructures as a two-dimensional array at various locations in the active layer matrix. High absorption enhancements of 53 and 61% were achieved with NSs and NCs, respectively, when they were incorporated at the top portion of the active layer. The influence of various passivation layers on the absorption enhancement was also investigated. The simulation results revealed that the absorption enhancement is mainly due to the near-field enhancement around the nanostructures and the backward reflection of incident light from the nanostructure array.

Gastrointestinal parasites of Asian elephants (Elephas maximus L. 1798) in south Wayanad forest division, Kerala, India.

Microscopic-coprological examination of Asian Elephant (Elephas maximus L., 1798) dung piles (n = 55) in South Wayanad Forest Division from March to August, 2017 revealed 74.5% prevalence of parasites in elephants. Ancylostoma sp. Anoplocephala sp., Strongyle type egg and Strongyloides sp. were the major parasites recorded. Strongyloides sp. and Strongyle type egg were observed more frequently (58.1%). Ancylostoma sp. and Anoplocephala sp. were constituted 1.8% each; mixed parasitic species infections were recorded. The frequency distribution of parasitic load in elephants showed skewed distribution of propagules. Centrifugal sedimentation and floatation methods of fecal examination of outer and inner regions of dung did not show significant difference in number of propagules. The highest number of parasitic propagules was recorded in floatation method. The number of propagules varied among dung samples of different herds collected from different localities. There were no relation between the parasitic load and age of elephants. The mean density of parasite eggs was higher in solitary animals (214.3 ± 155.4 epg) than herd elephants (147.78 ± 111.1 epg). Though parasitic load was higher in solitary males, based on the occurrence of parasites using logistic regression it was found that females had 1.83 times higher occurrence for parasitic infection than males. Both length and width of parasite egg size classes were used to classify into different taxonomic groups using discriminate function analysis. Three distinct size clusters were identified. Nematode and Cestode eggs were classified correctly with 95.7% accuracy. Since, the egg size was similar in nematode group separation into genus was difficult. Further, inclusion of stages of development of egg and larvae enable better separation.

Organic bistable memory devices based on MoO3 nanoparticle embedded Alq3 structures.

Organic bistable memory devices were fabricated by embedding a thin layer of molybdenum trioxide (MoO3) between two tris-(8-hydroxyquinoline)aluminum (Alq3) layers. The device exhibited excellent switching characteristics with an ON/OFF current ratio of 1.15 × 103 at a read voltage of 1 V. The device showed repeatable write-erase capability and good stability in both the conductance states. These conductance states are non-volatile in nature and can be obtained by applying appropriate voltage pulses. The effect of MoO3 layer thickness and its location in the Alq3 matrix on characteristics of the memory device was investigated. The field emission scanning electron microscopy (FE-SEM) images of the MoO3 layer revealed the presence of isolated nanoparticles. Based on the experimental results, a mechanism has been proposed for explaining the conductance switching of fabricated devices.